Monday, 11 April 2016 12:00

Deadly Charm of the Hanging Pitchers: Bandura

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Tropical pitcher plants attract insects for more than just the act of pollination. The hanging menace that makes up this intriguing predator entices its victims, whether they crawl or fly, through various means which have been a source of fascination for centuries.

Bandura, or Nepenthes distillatoria, is an endemic plant that has developed some of nature's most unique ways of survival in the tropical jungles of SriLanka. Contrary to the beliefs of westerners who arrived in the country during the colonial era, the flavourless fluid within the pitcher plants are not accumulated rain drops ready for human consumption - far from it, though the locals have long known of their medicinal value.

The unlikely-looking leaves rolled up to form the pitchers are the most intriguing aspect of this shrub-like climber, though do not be deceived. They emit a sweet scent that seduces an insect to an irresistible meal of nectar. Once attracted, its doom is sealed. The way out for the insect becomes a bleak and endless struggle of life and death. The inbuilt lid acts as a roof preventing any rain water which might dilute the liquid within the pitcher from seeping through, at the same time providing a surface for tiny crawling insects to take shelter, in an attempt to lure them into the soup of enzymes beneath. The lip at the entrance to the channel and the slippery inner walls are delicately and precisely manoeuvred for the kill.

This suggests the existence of a mutually -beneficial relationship between the pitcher plant and other forms of life

The pitcher of the plant has often been mistaken for the flower. Whereas its flowers on the one hand are waxy, tiny, and yellow in colour, they are much less attractive than the pitchers. Locally termed ‘Bandura', the endemic pitcher plant found in Sri Lanka was in fact the second species of Nepenthes, to be named according to standard forms of binomial nomenclature, in the early 18th century. Despite just the single species being discovered in Sri Lanka, we were taken by surprise at the sight we actually witnessed. There were quite evidently two distinct types of pitchers. Those much closer to the ground level were reddish in colour, with tiny tentacles on the wing-like appendages of the pitcher which served their purpose in encouraging the crawling insects to climb up effortlessly, while those hanging away from the ground level had no tentacles, were much greener in colour and even their lids opened in different directions. This was indeed a clear case of leaf dimorphism, where the same plant grows different types of leaves, to serve the plant's energy intake to its best advantage. The pitchers that were above ground level were without doubt intended to attract flying insects while those that were on ground level were designed for the crawlers.

The lowland wet conditions are ideal for them, and you are likely to witness this living, breathing, carnivore without too much trouble

Pitcher plants almost always grow in soil low in nutrition but where there is plenty of sunlight. These plants devour meat as a means of receiving as much nutrition as possible to absorb the essential nitrogen they need in order to survive. With little or no competition from other plants, the bandura are abundant in open areas where they catch the sun's rays. The lowland wet conditions are ideal for them, and you are likely to witness this living, breathing, carnivore without too much trouble along the side of the road at Labugama, Kalatuwawa, Athweltota, Gilimale, Kanneliya Forest Reserve, or the Sinharaja Forest. In many of these locations, villagers have been engaged in the small-scale commercial production of beautifully hand-woven goods such as baskets and vases, where the raw material needed is obtained straight from the hard stems of the pitcher plant.

Like the leaves, the enzyme juice of the pitcher does not necessarily mean death for all life forms. The sight of larvae swimming happily in the juice is quite a common one, proving that some organisms have clearly developed a natural resistance to the enzymes that bring doom to other insects. This undoubtedly suggests the existence of a mutually-beneficial relationship between the pitcher plant and other forms of life. Scientists have discovered many diverse associations between the pitcher plants and other animals, and this explains how successfully the pitcher has adapted its journey over time and in different habitats. Even the smallest amphibian of the old world, Microhyla borneensis, lay their egg within the juice of a bandura. Indeed, some pitcher plants have struck up a quid pro quo agreement with smaller mammals such as bats and shrews that come to feed on the insects that are attracted by the pitcher, and in turn the pitcher is rewarded with the nourishing nitrogen-rich excretory matter of these small mammals. Importantly, despite its carnivorous nature, the pitcher plant is not deadly for humans - except in the realms of fiction!

Words Nethu Wickramasinghe Photography L J Mendis Wickramasinghe

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